1. Field of the Invention
In general, the present invention relates to a receiving apparatus, a signal demodulating method, an antenna apparatus, a receiving system and an antenna direction adjusting method. In particular, the present invention relates to a receiving apparatus, a signal demodulating method, an antenna apparatus, a receiving system and an antenna direction adjusting method which are appropriate for adjusting the direction of an antenna for receiving radio waves broadcasted through satellites.
2. Description of Related Art
In recent years, a system for receiving radio waves broadcasted through communication and broadcasting satellites is becoming popular. In such a system, it is necessary to adjust the direction of an antenna thereof so that radio waves transmitted by the satellites can be received by the antenna correctly.
An invention relating to the adjustment of such an antenna is disclosed in Japanese Patent Publication No. Sho59-47883.
To be more specific, according to the disclosed invention cited above, radio waves transmitted by a satellite 1 are received by a parabola antenna 11 as shown in FIG. 5. A signal resulting from the reception of a radio wave by the parabola antenna 11 is converted into a signal having a predetermined intermediate frequency by an outdoor converter unit 12. The signal having the predetermined intermediate frequency is then supplied to an indoor converter unit 31 installed under the roof 21 of a house through a cable 15. The indoor converter unit 31 demodulates the intermediate frequency signal, outputting the result of the demodulation to a television receiver 32.
The direction of the parabola antenna 11 is adjusted by adjustment of a direction adjusting unit 13 so as to make the parabola antenna 11 correctly oriented toward the satellite 1. A meter 14, which allows an antenna adjusting person to know whether or not the parabola antenna 11 is correctly oriented toward the satellite 1 with ease, is provided on the outdoor converter unit 12.
The meter 14 works as follows. As is shown in FIG. 6, in the outdoor converter 12, a band pass filter (BPF) 41 extracts signals in a predetermined frequency band from a signal received by the parabola antenna 11. A signal output by the BPF 41 is then amplified by an amplifier 42 before being supplied to a frequency converter 43 for converting the signal into an output signal having a predetermined intermediate frequency which output signal is called an IF signal. The IF signal output by the frequency converter 43 is amplified by an intermediate frequency amplifier 44. A signal output by the intermediate frequency amplifier 44 is supplied to a signal splitting circuit 45 for transmitting the signal to the indoor converter unit 31 through a cable 15.
Part of the IF signal output by the intermediate frequency amplifier 44 is supplied to a detecting circuit 46 by the signal splitting circuit 45. Detecting the IF signal, the detecting circuit 46 outputs a direct current signal representing the level of the IF signal. The direct current signal output by the detecting circuit 46 is amplified by a direct current amplifier 47 before being supplied to the meter 14.
As a result, the level of the IF signal is displayed on the meter 14. While watching the display on the meter 14, the person adjusting the direction of the parabola antenna 11 makes the parabola antenna 11 oriented in such a direction toward the satellite 1 that the level of the IF signal is maximized.
By providing the meter 14 on the outdoor converter unit 12 as described above, the person adjusting the direction of the parabola antenna 11 can carry out adjustment so as to make the parabola antenna 11 oriented in a correct direction toward the satellite 1 by himself or herself with ease.
In such a conventional apparatus, however, the level of the IF signal is monitored at the outdoor converter unit 12, giving rise to a problem that the configuration of the outdoor converter unit 12 becomes complex and, thus, the price thereof becomes expensive.
On the top of that, since the level of the IF signal is monitored, it is impossible to identify which satellite is generating the radio wave being monitored in the case of a plurality of satellites 1 existing. As a result, it is feared that the adjustment causes the parabola antenna 11 to be oriented toward a wrong satellite by mistake.